Piezo-electric crystal



Aug. 30, 1932. c. w. HANSELL INVENTOR RENcE w Museu.

BY /w 265m IMU Filed Oct l llllll AZORNEY Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE CLARENCE w. HAN'sELL, or ROCKY POINT, NEW YORK, AssIGNOR 'ro RADIO CORPORA- TION or Aia/IE'RIOA7 A CORPORATION or DELAWARE PIEZO-ELECTRIC CRYSTAL Applica/apn meal october 2, 192s. sei-m1 No. 309,875.

' This invention relates to piezo-electric crystals, and more particularly to a method and means for reducing the wear of the crystal aswell as controlling the temperature of such crystals. y y

One difficulty experienced with piezo-electric crystals is the'change in'resonance' frequency caused by the gradual change in thickess resulting lfrom wear of the crystal against its electrodesduring vibration. As a practicalmatter I find that this wear takes place regardlessof the quality ofthe finish ofthe crystal and the electrodes. It is an Object of my invention to reduce such wear, and to this end I keep the crystal from contact with its electrodes by passing a stream of gas between the crystal and the electrodes.

' For :constant frequency a piezo-electric crystal must bekept at constant temperature, but experience has shown that it is not entirely satisfactory. merely to keep the crystal holder, or some larger ,chamber in which the entire crystal holder ismounted, at a constant temperature, for there is considerable heat insulation between the crystal and the holder, and they do not necessarily remain at the same-temperatures, especially 4owing' to the fact that thecrystal itself dissipates considerable heat during vibration. A'further object of my invention is to providetemperature control vof -the crystalitself, and lthis I doby passing a stream of gas around the crystahancl regulating the ltemperature of the gas. Of course, in practice the same stream rof gas may serve for both the reduction of Wearand the regulation of the crystal temperature. i

' The'rapid vibration of a crystal against even a. gas medium is undesirable, andto reduce this disadvantage is another object of my invention, which I accomplish by moving the aforesaid stream of gas by suction in order tjo rarify the gas surrounding the crystal. For the sake of economy and simplicity air may be used as the gas circulated around the crystal, but in cases where a closed circulating system is feasible hydrogen or helium may well be used because of the great heat conductivity and the low density of these gases.

A further object of my invention is to proyide the desired suction head without resortmg to special mechanically driven means. The crystal ordinarily is used for the control of transmitters employing vacuum tubes of suficient power to be provided with water cooling and a circulating system for the cooling water. Itakeadvantage of this fact by coupling the air circulating system of the crystal to a Y branch in the water circulating s stem, so that the suction head caused by the ow of cooling vWater draws the air from around the crystal.

The invention is described more in detail in the following specification, which is accompanied by drawing in which Figure 1 is one form of my invention; and

Figure 2 is a preferred modification.

Referring to Figure 1 there is a crystal 2 which is situated in a crystal holder 4, comprising upper and lower electrodes 6 and 8 respectively. These electrodes are electrically insulated by a. suitable insulation portion 10.

The electrodes, it will be seen, are relatively thick, and are pierced by relatively long and constricted air inlet passages 12. To complete the air circuit an air outlet passage 14 is provided, which opens into the crystal chamber between the electrodes.

The entire crystal holder 4 is enclosed Within a chamber 16. A blower 18 is provided for increasing the pressure Within the chamber, while the conduit 14 leads without the chamber, and,'if a gas other than air is employed, it may lead, as shown, to a radiator 15 and thence back to the blower 18. A pressure regulating device 2O is provided for so controlling the blower 18 as to maintain a constant pressure within the chamber. A heating arrangement 22 is provided within the 90 chamber, and responds to a temperature control device 24, in Order to maintain the gas in the chamber at a constant temperature. Of course, a suction blower could be used and in such case it would preferably be connected to the outlet pipe 14. Also, a heating device and thermostatic control therefor may be inserted directly in the circulating conduits, as has been indicated by the elements 20 and 22.

Attention is now directed to Figure 2, in 100 which there is a crystal 2 situated inside of a crystal holder 4, provided with upper and lower electrodes 6 and 8, electrically insulated by an insulation bushing 30. As before, the electrodes are made massive in thickness, and are pierced by relatively long and constricted 'air inlet "passages l2. Air outlet passages 34 are provided in the body of the crystal holder, which consists essentially of the lower electrode. so massively constructedV that it encloses the upper electrode. In this case the air is moved by suction, and

the suction is provided by a Y branch V36 insertedin the cooling water circulating system 38 of the water cooled vacuum tube 40, which -itself is part. of an oscillator, or amplilier,`or transmitter, the frequency of which is initially'det-ermined by the crystal.

Si) (i In the arrangement here shown it is possible to obviate the use of a chamber for enclosing the crystalholder, and for this purpose the air inlet passages l2Y are made sutlicientlyV long-and constricted'so thatl they serve not only the purpose ofreducing the pressurein the crystal chamber, but also of insuring that the temperature rofthe air, when it reaches the crystaly chamber, has become i substantially thatV of the, electrodes. `With such an arrangement the'crystal may be kept at a constant temperature by keeping the crystal holder at aV constant'temperature, and there is no danger. ofV heat insulation between the crystal. and the crystal holder spoiling the attempted temperature control. n

The crystal holder is heated bya coil of resistance wire indicated invsection at 42, and energized from a suitable source of heating current 44 when the relay 46 closes the heating-circuit. The relay in turn is actuated in response to an electrical circuit which is itself closedfo-r opened by a thermometer 48.v The reservoir of this thermometer consists of a hollow. annular ring 50, which is embedded in the body of the crystal holder 4, or the n liquid may be directly in Contact with the body of, the crystal holder, and the latter provided with'a thermometer stem. To provide foraccidental over heating an overflow bulb 52 is added. When the temperature of the Q crystal -holderrises `the mercury in the bulb expands and rises in the tube 48, and, contacting with an electrod-e`54, actuates the relay 46 to open the heating circuit.

What I claim is: Y l. .Themethodot reducing the wear of a piezo-electric crystal which includes keeping the crystal from contact with its electrodes by passing'a stream of gas between the crystal and the electrodes. Y Y

v2. rl`he method of reducing the wear of a piezo-electric crystal which includes passing a stream ot' gas between the crystal and the electrodes, and'moving the stream of'gas by suctionin'o'rder to rarefy the gas surround- .E the crystal.

3. The method of reducing the wear of a piezo-electric crystal and governing its temperature which includes keeping the crystal from contact with its electrodes by passing a stream of gas between the crystal and the electrodes, and regulating the temperature of the gas.

4. An arrangement for reducing the wear of a piezo-electric crystal comprising the crystal, a holder, electrodes mounted `in, said t against'the crystal, a crystal.disposed be-l tween said electrodes,'and means toregulate.

the temperature ofthe gas. f

6. An arrangement for reducing the wear. and controlling the temperatureof a piezoelectriccrystalcomprising a crystal holder, electrodes mounted in said holder and being provided with means to pass a stream of gasy between the crystal and the electrodes to prevent the crystal from resting 'onY the electrodes, a crystal disposed Vbetween said electrodes and means tocontrol the ter'nperature of the gas.

7. In combination, a crystal holder having electrodes provided with air passages therethrough, said holder being provided with other passages opening into the crystal cham.- ber between the electrodes to complete the air circuit, andy meansA Vfor. Ycirculating airV through the air circuit anda crystal disposed.'v

between said electrodes.v

with air inlet passages therethrough, air out'- let passages opening into the crystal chamber between the'electrodes, and means to apply a suction head to the outlet passages in order to cause a stream of rarelied airtol iow bet-Ween the electrodes and the crystal and. a crystal disposed between said electrodes.

f 9. In combmation, a crystal holder Vhaving relatively thick electrodespierced by relatively long and constricted air inlet passages, air outlet" passages opening into the crystal chamber betweenv the electrodes, a crystal disposed between said ele'ctrodes, means for causing air circulation around the crystal from thel inlet to` the outlet passages,: and automatic means for controlling theY temperature of the electrodes in'order to regulate 8. In combination, a crystal holder havingV 119 a crystal chamberv and electrodes` provided the temperature of the air flowing around the crystal.

10. A piezo-electric crystal holder comprising electrodes mounted in said holder, one of said electrodes being removable to permit the insertion and removal of a piezoelectric crystal vibrator in said holder, said electrodes being provided with air passages to permit'l a flow of air into and out of the said holder, whereby the temperature of the said crystal may be controlled.

CLARENCE W. HANSELL. 

